Your Question

If a man is diagnosed with CBAVD and is looking to father a child with his wife through in vitro fertilization, how important is it to find out if the CBAVD was caused by a mutation in the CFTR gene? How much of an increased risk is there to have a child with cystic fibrosis when CBAVD is caused by a CFTR mutation?

Our Answer

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Is it important to determine if CBAVD is caused by CFTR mutations in males who want to have children?

Since almost all males with cystic fibrosis (CF) also have CBAVD, it was suspected (and later confirmed) that isolated CBAVD has a common genetic origin with CF. Isolated CBAVD has been proposed as a primarily genital form of CF. Studies have shown that most men with CBAVD have two different CFTR mutations (and are referred to as compound heterozygotes), with at least one being a "mild" mutation.[1] A mild mutation in the CFTR gene may lesson the amount of normal protein produced by the gene but, not render the gene non-functional. Some males with CBAVD have a mild mutation in one copy of the CFTR gene in each cell and a more severe, CF-causing mutation in the other copy of the gene.[2]

Because most males with CBAVD are able to father children with assisted reproduction, CFTR mutations may be transmitted to an affected male's child, thus possibly increasing the child's risk to be a CF carrier or to have CF. Most men with CBAVD have detectable CFTR mutations; therefore, genetic testing should be offered to affected males before undergoing assisted reproduction. Identifying CFTR mutations in the affected male and determining the genetic status of his partner allows for a better evaluation of the genetic risk to a child. Although no official consensus has been reached regarding which mutations should be evaluated (only the most common mutations versus all mutations), most experts recommend screening of all CFTR mutations.[1]

Individuals interested in genetic testing for CBAVD or CF should speak with a genetics professional.

Last updated: 4/8/2013

Is a man with congenital bilateral absence of the vas deferens (CBAVD) at an increased risk to have a child with cystic fibrosis?

Males with CBAVD caused by mutations in the CFTR gene have an increased risk of having a child with cystic fibrosis (CF), which is inherited in an autosomal recessive manner. If CBAVD is not caused by mutations in CFTR, the risk of having a child with CF is not increased.[3]

About 80 mutations in the CFTR gene have been identified in males with CBAVD. Most males with CBAVD have a mild mutation in at least one copy of the gene in each cell; a mild mutation allows the CFTR protein to retain some of its function. Some males with CBAVD have a mild mutation in one copy of the gene and a more severe, CF-causing mutation in the other copy of the gene.[2]

The exact risk of CF to offspring of a male with CBAVD depends on the genetic status of the affected male and his partner and cannot readily be predicted without this information. Males with CBAVD sometimes have only one identifiable CFTR mutation, complicating the testing and interpretation of results in family members. Prenatal testing for pregnancies at increased risk is possible, but only after the disease-causing mutations in the CFTR gene are identified in both parents. When one parent is known to be a CFTR mutation carrier and the other parent has tested negative for CFTR mutations, there is no additional testing available to clarify the genetic status of the fetus.[4]

Individuals interested in learning more about genetic testing or genetic risks to themselves or family members should speak with a genetics professional.

Last updated: 4/8/2013

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:

The American Society of Human Genetics maintains a database of its members, which includes individuals who live outside of the United States. Visit the link to obtain a list of the geneticists in your country, some of whom may be researchers that do not provide medical care.